This invention relates to combustion systems and particularly to a safety device for shutting down a combustion system when a flame rollout condition occurs at the burners of the combustion system. Specifically, this invention relates to an inexpensive, redundant safety device for detecting a flame rollout condition at the burners of a combustion system and for discontinuing the flow of fuel to the burners of the combustion system when the flame rollout condition is detected.
A combustion system, such as a furnace, may, under conditions of insufficient or contaminated combustion air, or pressure buildup in the combustion chamber, develop what is known as a flame rollout condition. In this condition, the fuel-air mixture burns steadily outside the combustion chamber at the location of the burners of the combustion system.
Furnaces normally include a thermal fuse, electropyrotechnic link, or a flame sensor for use in the control wiring of the furnace to detect and respond to a flame rollout condition. These devices open an electrical circuit to a fuel supply valve which controls the flow of fuel to the furnace should temperatures in the control compartment, where the control wiring is located, exceed a certain value. Thus, these devices operate as thermal circuit breakers to open the electrical circuit to the furnace fuel supply valve thereby closing the valve and shutting down the furnace when a flame rollout condition occurs.
These thermal circuit breaker devices are special safety devices which are made a part of a combustion system but which are not necessary for the normal operation of the combustion system. Thus, although these special safety devices provide an important safety function, they increase the cost and complexity of the combustion system without increasing the operational performance of the system. Also, like any device, there is a possibility that the special safety device can malfunction, or be defeated by tampering.
It is desirable for a combustion system to have a redundant safety means for detecting and responding to a flame rollout condition. The use of a redundant safety means increases the probability of successfully detecting and responding to a flame rollout condition. However, the use of an additional special device, such as a thermal circuit breaker device, would further increase the cost and complexity of a combustion system without increasing the operational performance of the system. Therefore, it is advantageous to provide a redundant safety means for a combustion system for detecting and responding to a flame rollout condition without increasing the cost and complexity of the combustion system.